Single and simultaneous adsorption of methyl orange and p-chlorophenol on organo-vermiculites modified by an asymmetric gemini surfactant

The superiority of asymmetric gemini surfactant over the symmetric one is unveiled in case of organo-vermiculite (organo-Vt) for the first time. A common asymmetric gemini surfactant [C22H45(CH3)2N+(CH2)2N+(CH3)2C10H21]Br2 (marked as 22-2-10) was adopted as modifier onto the vermiculite (Vt) to prepare adsorbent targeted at methyl orange (MO) and p-chlorophenol (PCP) in single and/or binary systems. The superiority of surfactant asymmetry on the structure of organo-Vt adsorbents was disclosed by larger interlayer spacing, more modifier loading, higher surfactant availability as well as the stronger adsorption capacity of organo-Vt modified by 22-2-10 (22-2-10-Vt) compared with organo-Vt modified by the corresponding symmetric modifier [C16H33(CH3)2N+(CH2)2N+(CH3)2C16H33]Br2 (16-2-16-Vt). Effective retention of MO (142 mg g−1) and PCP (85 mg g−1) in single system were fitted by the pseudo-second-order, Langmuir and intra-particle diffusion models. Particularly, organic-matter-corrected sorption coefficient (KOM) was introduced to verify the partition process, which was found dominant in the adsorption processes and further promoted by hydrogen bond, intermolecular interaction and π-π interactions. The practical feasibility of 22-2-10-Vt was achieved in binary system, where the total adsorbate retention (0.74 mmol g-1) was higher than that in single systems (0.54 or 0.31 mmol g-1 for MO and PCP, respectively). An orderly gradient adsorption process was proposed in the binary system due to the stronger hydrophobicity of MO than PCP. The adsorbed adsorbents were regenerated by ethanol at least for three cycles in binary systems. The results obtained could not only throw lights on asymmetric modifiers and the related analogues, but also extend to the feasibility of organo-Vts in the multi-component water environment.